1. Technical Field
The present invention relates to a strut for use in a suspension system, and particularly relates to controlling the spring and the damping characteristics of a vehicle strut.
2. Background Art
A multitude of struts for use in suspension systems are known in the art. Some struts use pressurized air or gas to dampen relative movement between parts. Other struts use elastomeric spring assemblies defining liquid chambers to provide the damping. Some struts include a combination of elastomeric spring assemblies, pressurized gas, and pressurized liquid. Certain known struts attempt to provide high deflection, a soft spring rate, and maximum load carrying capacity.
A known vehicle strut is disclosed in U.S. Pat. No. 3,658,314. The strut of U.S. Pat. No. 3,658,314 combines the functions of a vehicle shock absorber and a vehicle compression spring. In one embodiment of U.S. Pat. No. 3,658,314 shown in FIG. 7, the strut includes an inner tubular member and an outer tubular member which is coaxial with the inner tubular member. Each tubular member defines a respective fluid chamber having fluid contained therein. A valving member divides the fluid chamber associated with the outer tubular member into two chamber portions. Orifices allow fluid flow between the fluid chamber associated with the inner tubular member and one portion of the fluid chamber associated with the outer tubular member. The strut further includes two elastomeric spring members which are serially arranged along the longitudinal central axis of the strut. Each elastomeric spring has a different spring rate. One elastomeric spring is secured to and between the inner tubular member and the outer tubular member. The other elastomeric spring is secured to the outer tubular member and an adjacent support.
When relative movement occurs between the inner tubular member and the outer tubular member, the elastomeric spring between the tubular members compresses or expands depending upon the direction of relative movement of the tubular members. This causes fluid flow between the different fluid chambers through the orifices. A fluid flow is also established between the two chamber portions associated with the outer tubular member through the valving member. The volumetric relationship between the different fluid chambers changes when these fluid flows are established. The result is that the energy of the relative movement between the two tubular members is absorbed and damped.
Another vehicle strut is disclosed in U.S. Pat. No. 3,955,807. The strut of U.S. Pat. No. 3,955,807 includes a cylinder and a piston axially movable within the cylinder. The cylinder and the piston define first and second fluid chambers in fluid communication with each other. The strut further includes a spring unit having a pneumatic spring chamber and a third fluid chamber in fluid communication with the first fluid chamber. An elastomeric diaphragm separates the pneumatic spring chamber and the third fluid chamber. A disc-shaped elastomeric spring is disposed within the third fluid chamber.
When a compression load is applied to the strut, the cylinder and the piston move relative to each other. The fluid pressure in all three fluid chambers increases. When the fluid pressure in the third fluid chamber increases above a predetermined amount, both the elastomeric diaphragm and the elastomeric spring deform in response thereto. The elastomeric diaphragm compresses against the pressure in the pneumatic spring chamber to damp and absorb the energy of the compression load.